you can do a magnetic model of this to get something quantitative.

It is going to depend on the circuitry connected to the receiving bond wire for sure, so a simple number answe can not be given.

One comment - it is significant and is frequently an issue in a noise coupling scenario.

Dear RobG,
are two bond wires are differential? or not. In general Mutual coupling decreases to less value if the horizontal distance between two wires> 4*wire diameter, in your case distance is around 400um which is Quite high compared to bond wire size(in my case the are around 60um).

Of course this approximation depends on what is the hight from the ground plane and shape of the wire ( the above approximation is for the rectangular waveguide, it may be slightly differ for circular shape)

Thanks,
Raj.

I found page 38 of "Digital System Engineering" by Dally and Poulton, which suggest k=~0.3, which gives a result similar to what I am seeing using the mind device to couple two inductors.

A link is here, although I don't know how stable it will be:
http://books.google.com/books?id=oDWRAxCU-g8C&pg=PA38&lpg=PA38&dq=coupling+coeff...

carlgrace wrote on Jan 30^th, 2014, 10:05am:


Thanks - those data points help everyone. A few things conspired to cause the problem, all related to egos and an overly aggressive schedule of course. It is comforting to be able to reproduce the negative results in simulation with this sort of information.

As an aside and lesson learned, although I didn't like it from the start, I didn't go bananas because the pads were at the corners, thus perpendicular. They also had ground pads between them. Well, the ground pads were downbonded to the paddle and offered no shielding. Furthermore, even though the two lines in question were perpendicular on the chip, in the package the bond wire went to the package corners so they were the longest wires and almost perfectly parallel. You couldn't have picked a worse configuration!

Correct me if I'm wrong, but I don't think adding a ground wire between the two leads would help since it is magnetic coupling. We used LVDS this time so the fields should cancel, but most importantly we treated the clock like the analog input that it is and kept it far from the digital.

Quote:


Hi RobG,


my previous group did quite a bit of study on this a while back so I can share a little of my experience. The coupling coefficient of 0.4 is quite reasonable. Also, regarding the perpendicular bondwires, sometimes it looks like the bondwires are perpendicular, but from a 3D perspective it turns out that they're not that perpendicular. This is more true when the chip is quite high so although the bondwires appear to be going in different directions, it turns out that they're both just going downwards.

As for putting ground downbonds in between, it can help, but as I remember you need to be careful. Basically inductance is always calculated around the whole loop, otherwise it is just partial inductance. Therefore you need to consider the return path. If you use a ground bondwire close to your signal bondwire, and they are tightly coupled, then the loop inductance will be reduced. The lower inductance will result in less coupling to other bondwires.

However, if you share the ground bondwire with other circuits, then you might end up just coupling noise through the shared ground. Also, the ground bondwire must be a current return path. If you just leave one end dangling it may not have any effect.


Aaron

rule of thumb - iif there is any signal on the leadframe, it will couple into the front end of an RF LNA or into the externally placed VCO filter of a PLL.

Anywhere on the leadframe, not just beside each other.

No formulas, just  seen a lot of learning experiences.